A ball grid array (BGA) package is a type of packaging for integrated circuits (ICs), such as a microprocessor or memory cell array. BGA packages permanently mount to a board or other package with balls of solder that are disposed in a grid layout over the entire surface area of one or more side of the package. While BGA technology is popular for high connection density, high heat conduction, and short, low-inductance connections, a variety of issues limit surface mount yield.
One issue is package warpage in which the package becomes strained and one or more connections are left open. Although a variable ball height (volume) would be able to compensate for package warpage, for example with taller (larger) balls at the package edge and shorter (smaller) balls near the package center, varying the size of the balls within a package is an expensive proposition for the standard ball pick-and-place technology that relies on all balls to be of a same nominal size. A multi-pass process might be employed, for example where smaller balls are placed first followed by larger balls. However, even if only a few different ball sizes were to be used, multi-pass processes would not only be costly, but also marginal with respect to yield as balls placed in a prior pass might be displaced during the subsequent pass.
Another issue is the need to avoid the application of flux or solder paste (which is employed to hold the balls in place during the pick-and-place operation) in regions of the package where land-side components (LSCs) are located. LSCs, such as capacitors, etc. are typically accommodated by providing a pocket in the stencil employed during the flux or paste printing process. The presence of these pockets can limit the minimum spacing between BGA balls and the LSCs and there is a need to scale down this spacing as package form factors continue to shrink.